Heating units such as wood and other fossil-fuel combustible material burning stoves, hot water radiators and the like disseminate heat into surrounding space by radiation and by convection of thermal air currents circulating around the unit. Warm air distribution from the unit may be enhanced by means of an air blower or fan suitably placed on or adjacent the unit. Presently, such air circulating fans are powered by electric battery or mains power supply.
It is known through the so-called “Peltier Effect” that when a direct electric current is passed through a thermoelectric couple, heat will be absorbed at one end of the couple to cause cooling thereof, while heat is rejected at the other end of the couple to cause a rise in temperature. By reversing the current flow, the direction of heat flow will be reversed.
Thermoelectric modules are forms of a thermoelectric couple and, typically, comprise an array of semiconductor couples (P and N pellets) connected electrically in series and thermally in parallel, sandwiched between metallized ceramic substrates.
In a reverse manner, by the so-called “Seebeck Thermocouple Effect”, a thermoelectric module behaves like a simple thermocouple in generating an electric potential across its terminals if a temperature gradient or thermocline is provided across the module when in an open circuit mode. Thus, electric power is generated as a function of the temperature difference between both ends of the module.
Pertinent prior art comprises a demonstration model of a power generation module powering an air circulation fan disclosed by Tellurex Corporation, Michigan, U.S.A. The Tellurex Corporation self-powered fan comprises a hot end heat exchanger heated by a hand-held propane torch, electric motor, fan blades, a cold end heat exchanger and a thermoelectric module sandwiched in thermal contact between the two heat exchangers and in electric contact with the electric motor. In this demonstration model, the module is heated by a propane torch to merely demonstrate current generation while requiring a hand held pyrometer to prevent overheating and destruction of the module. It is clear from this demonstration model that it could not be satisfactorily and reliably used to circulate heat from a hot surface, since sufficiently high temperatures of the hot surface sufficient to provide an effective air circulation effect would cause the thermoelectric module to simply overheat and be destroyed. Further, the orientation of the fan and the cool end heat sink are so located relative to the heat source as to cause passage of the hot gases on the hot side of the thermoelectric module around and through the cool end heat sink. Thus, the Tellurex Corporation demonstration model has no practical and reliable utility as a warm air circulating fan if placed on a heated surface.
U.S. Pat. No. 5,544,488, issued Aug. 13, 1996 to Reid, Randall H. describes an air circulation fan powered only by a thermoelectric module obtaining heat available at the heated surface of a heating unit, such as the top of a stove, can provide useful warm air circulation, notwithstanding the extremely low efficiency of conversion of thermal energy to electrical energy inherent in the aforesaid Seebeck Thermocouple Effect. U.S. Pat. No. 5,544,488 teaches that by judicious selection of components and the physical arrangement of these components to constitute a hot air circulation fan suitable efficacious warm air circulation is reliably and safely obtained. Thus, not only is warm air propelled forward from the unit to provide warm air circulation but that incoming cooler air pulled by the fan operates to enhance cooling of the heat sink cool end and, when appropriate, the hot end of the thermocouple module to provide reduced risk of damage through overheating of the thermocouple module.
Further, U.S. Pat. No. 5,544,488 teaches that an air circulation fan powered only by a thermoelectric module cooled at the cooling surface of a cooling system, such as, for example, provided by ice/water or a refrigeration system can provide useful air circulation, notwithstanding the extremely low efficiency of conversion of thermal energy to electrical energy inherent in the Seebeck Thermocouple Effect. Judicious selection of components and the physical arrangement of these components to constitute an air circulation fan suitable efficacious air circulation is reliably and safely obtained
There is, however, a need for such self-powered heat transfer fans having improved performance characteristics.